The invention relates to a spring assembly for an injection device, to a corresponding injection device and to a method for assembling these injection devices. In particular, the invention relates to an improved drive unit for an injection device and to a method for assembling this drive unit in the injection device.
Here, the term “drug” comprises any flowable medical formulation which is suitable for controlled administration through a means such as, for example, a cannula or hollow needle, comprising, for example, a liquid, a solution, a gel or a fine suspension containing one or more medical active substances. Drug can refer to a composition with a single active substance or to a premixed or co-formulated composition with a plurality of active substances from a single container. Drug or product comprises medicines such as peptides (for example, insulins, insulin-containing drugs, GLP-1-containing preparations as well as derived or analogous preparations), proteins and hormones, biologically prepared or active substances, active substances based on hormones or genes, nutrition formulations, enzymes and other substances either in solid (suspended) or liquid form but also polysaccharides, vaccines, DNA or RNA, or oligonucleotides, antibodies or parts of antibodies as well as suitable base substances, adjuvants and carrier substances.
WO2014/170267 discloses injection devices with a compact energy storage. The energy storage comprises at least two mutually connected spiral springs which can have sufficient energy stored, i.e., which are pretensioned, in order to empty an entire drug container. The document discloses no details on how the spiral springs can be pretensioned.
WO2014/154491 discloses an energy storage unit for an administration device. This energy storage unit comprises a pretensioned pressure spring, wherein the unit has a transport locking mechanism which is intended to prevent accidental activation of the energy storage unit. For the administration of viscous drugs, compressive springs have to have large and long dimensions, so that the administration devices also have to have larger dimensions. Then, in order to be able to achieve a regular administration of a drug, pressure springs have to be pretensioned sufficiently, which, in the case of the use of finished syringes made of glass as a drug container, increases the risk of glass breakage due to triggering of the administration device.
Therefore, it would be desirable to have energy storage units available that can be transported easily with stored energy and that can also be fitted geometrically into known administration devices.